Prosthesis wearers who require a knee prosthesis have to accept compromises in terms of the damping of the flexion and extension in the configuration of their prosthesis, since passive prosthetic knee joints are optimized only for certain uses, and, therefore, significantly different movement patterns are either not possible or are only possible with extraordinary difficulty. Thus, the movement sequence for walking on level ground, for which most of the passive prosthetic knee joints with flexion and extension damping are designed, requires substantially different damping characteristics than those for climbing stairs. Therefore, with the conventional knee joint prostheses, the prosthesis wearer climbs stairs by a procedure in which, standing in front of the stairs, the healthy leg is lifted onto the first step and the contralateral leg is then pulled up onto this same step. The walking speed may possibly be increased if the healthy leg is placed on every second step, but this is very demanding.
In conventional knee joint prostheses designed for walking on level ground, the necessary low extension damping of the prosthetic knee joint has the effect that, when climbing stairs, an abrupt extension takes place when pushing oneself upward, and this subjects the prosthesis wearer to an unacceptably high load. Balancing of the leg provided with the prosthesis is also not possible, because three joints, namely the ankle joint, the knee joint and the hip, are arranged one above the other and the prosthesis wearer can only directly control the hip joint. Even when lifting the prosthetic foot in order to reach the next step up, the problem arises that the prosthetic foot is moved onto the riser or onto the underside of the next step up, since the necessary flexion damping in the swing phase control for walking on level ground makes it impossible to reach the top face of the next step up. The flexion drive mechanism provided in active knee joints for the purpose of lifting the foot and the extension drive mechanism for straightening the knee and lifting the body via the leg provided with the prosthesis is very complicated and very heavy. Furthermore, the swing phase control for walking on level ground is very limited in these active prosthetic knee joints.